1. Field of the Invention
The invention relates to a tapping screw including a head, a self-tapping thread portion and a drilling point. The drilling point has a pair of approximately axially extending flutes which are located diametrically opposite each other relative to the shank axis and include clearing surfaces and cutting surfaces. The cutting surfaces end in cutting edges facing the point of the screw and lateral outer cutting knives. With respect to a plane extending through a cutting edge and the corresponding cutting knives, each flute defines a concavely rearwardly arched indentation.
2. Description of the Prior Art
Tapping screws of the above-described type have become known in various embodiments. Since the cutting surfaces located immediately adjacent the cutting edges or cutting knives of these tapping screws are concavely arched, the cutting knives or cutting edges may break, particularly if relatively hard materials are to be drilled. In addition, the chips removed by drilling may stick to the cutting surfaces and may fail to separate from the sides of the approximately axially extending flutes. This may lead to difficulty because the cutting efficiency of the drilling tip is reduced. Consequently, a drilling point damaged in the manner described above or clogged with chips may make it impossible to conclude the drilling procedure, so that possibly new screws are needed for use in the same borehole.
Therefore, it is the primary object of the present invention to provide a tapping screw in which the drilling efficiency is substantially increased and in which the danger of breakage of the cutting edges or cutting knives and sticking of chips to he cutting surfaces is practically eliminated.